Prosecutors urged a UN-backed genocide tribunal to deny bail to the former head of the Khmer Rouge's largest torture center, saying his release could pose a threat to public order in Cambodia.

Prosecutors urged a UN-backed genocide tribunal on Wednesday to deny bail to the former head of the Khmer Rouge's largest torture center, saying his release could pose a threat to public order in Cambodia.

Kaing Guek Eav, alias Duch, is charged with committing crimes against humanity as the commandant of the regime's notorious Tuol Sleng prison. He is one of five people held in connection with the communist regime's brutal 1970s rule of Cambodia.

Duch has been in custody since 1999. He became the first defendant to appear before the long-awaited tribunal when his bail hearing opened on Tuesday. His defence lawyers argued that Duch's human rights were being violated by his long detention and he should be freed on bail ahead of trials expected to start next year.

Prosecutors called Duch a "flight risk" and urged the court on Wednesday to keep him behind bars, for his own safety and in the interest of public order.

If Duch were released he could be harmed both by "accomplices wishing to silence him and by the relatives of victims seeking revenge," Robert Petit, a prosecutor from Canada, told the court.

Petit added that "the entire public order (could) be jeopardized" if the ageing Khmer Rouge official was freed.

The Khmer Rouge regime was blamed for the deaths of an estimated 1.7 million people during its reign from 1975-79. Many have said they feared the surviving Khmer Rouge leaders might die before being brought to justice, as did the movement's notorious leader, Pol Pot, in 1998.